package 尚硅谷;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;

/**
 * @author zhangmin
 * @create 2022-03-23 19:34
 * 手写一个自旋锁
 *      spinlock，是指尝试获取锁的线程不会立即阻塞，而是采用循环的方式去尝试获取锁，这样的好处是减少线程上下文切换的消耗，缺点是循环会消耗CPU
 */
public class SpinLockDemo {
    //原子引用线程,初始值为null
    AtomicReference<Thread> atomicReference=new AtomicReference<>();
    public void myLock(){
        Thread thread=Thread.currentThread();
        System.out.println(Thread.currentThread().getName()+"/t come in");
        while (!atomicReference.compareAndSet(null,thread)){
            //第一次进入时，不会进入while循环内
        }
    }
    public void UnLock(){
        Thread thread=Thread.currentThread();
        atomicReference.compareAndSet(thread,null);
        System.out.println(Thread.currentThread().getName()+"/t invoked myUnlock");
    }

    public static void main(String[] args) {
        SpinLockDemo spinLockDemo=new SpinLockDemo();
        new Thread(()->{
            spinLockDemo.myLock();
            try {
                TimeUnit.SECONDS.sleep(5);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            spinLockDemo.UnLock();
        },"AA").start();

        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        new Thread(()->{
            spinLockDemo.myLock();
            spinLockDemo.UnLock();
        },"BB").start();
    }

}
